au­tonum – Au­to­matic equa­tion ref­er­ences

The pack­age ar­ranges that equa­tion num­bers are ap­plied only to those equa­tions that are ref­er­enced. This op­er­a­tion is sim­i­lar to the showon­lyrefs op­tion of the pack­age math­tools.